title: Fed-state clamp stimulates cellular mechanisms of muscle protein anabolism and modulates glucose disposal in normal men.
abstract: Since maximum anabolism occurs postprandially, we developed a simulated fed state with clamped hyperinsulinemia, physiological hyperglycemia, and hyperaminoacidemia (Hyper-3) and explored muscle cellular mechanisms. Whole body [1-(13)C]leucine and [3-(3)H]glucose kinetics in healthy men were compared between hyperinsulinemic, euglycemic, isoaminoacidemic (Hyper-1, n = 10) and Hyper-3 (n = 9) clamps. In Hyper-3 vs. Hyper-1, nonoxidative leucine R(d) [rate of disappearance (synthesis)] was stimulated more (45 +/- 4 vs. 24 +/- 4 micromol/min, P < 0.01) and endogenous R(a) [rate of appearance (breakdown)] was inhibited similarly; hence net balance increased more (86 +/- 6 vs. 49 +/- 2 micromol/min, P < 0.001). Glucose R(d) was similar; thus Hyper-3 metabolic clearance rate (331 +/- 23 vs. 557 +/- 41 ml/min, P < 0.0005) and R(d)/insulin (M, 0.65 +/- 0.10 vs. 1.25 +/- 0.10 mg.min(-1).pmol(-1).l, P < 0.001) were less, despite higher insulin (798 +/- 74 vs. 450 +/- 24 pmol/l, P < 0.005). In vastus lateralis muscle biopsies, phosphorylation of Akt (P = 0.025), mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70(S6K1); P = 0.008), S6 (P = 0.049), and 4E-binding protein 1 (4E-BP1; P = 0.001) increased. With decreased eukaryotic initiation factor-4E (eIF4E).4E-BP1 complex (P = 0.01), these are consistent with increased mTOR complex 1 (mTORC1) signaling and translation initiation of protein synthesis. Although mRNA expression of ubiquitin, MAFbx 1, and MuRF-1 was unchanged, total ubiquitinated proteins decreased 20% (P < 0.01), consistent with proteolysis suppression. The Hyper-3 clamp increases whole body protein synthesis, net anabolism, and muscle protein translation initiation pathways and decreases protein ubiquitination. The main contribution of hyperaminoacidemia is stimulation of synthesis rather than inhibition of proteolysis, and it attenuates the expected increment of glucose disposal.
authors.affiliation: School of Kinesiology and Health Science, York University, Toronto, Ontario, Canada.
authors.forename: Olasunkanmi A J
authors.initials: OA
authors.lastname: Adegoke
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Chevalier
authors.forename: José A
authors.initials: JA
authors.lastname: Morais
authors.forename: Réjeanne
authors.initials: R
authors.lastname: Gougeon
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Jefferson
authors.forename: Simon S
authors.initials: SS
authors.lastname: Wing
authors.forename: Errol B
authors.initials: EB
authors.lastname: Marliss
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000328:Adult; D000596:Amino Acids / Q000008:administration & dosage / Q000097:blood; D001706:Biopsy; D018797:Cell Cycle Proteins; D005947:Glucose / Q000378:metabolism* / Q000493:pharmacokinetics; D015309:Glucose Clamp Technique / Q000379:methods; D006801:Humans; D007930:Leucine / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D019518:Postprandial Period; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000096:biosynthesis / Q000235:genetics; D058570:TOR Serine-Threonine Kinases; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D009124:Muscle Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin; C440907:FBXO32 protein, human; D044843:SKP Cullin F-Box Protein Ligases; C440908:TRIM63 protein, human; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D007930:Leucine; D005947:Glucose